JP2012167854A - Heat transfer tube for falling liquid film evaporator, and turbo refrigerator using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure that a heat transfer tube is wet on the outer surface thereof with refrigerant, thus improving the heat exchange performance of the heat transfer tube.SOLUTION: The heat transfer tube formed into a tubular shape and configured to boil and evaporate falling liquid on the outer surface thereof, includes: a plurality of continuous fins formed annularly or helically in a circumferential direction of the outer surface of the heat transfer tube; and a plurality of cavities formed such that a tip of each of the fins is bent to be substantially parallel to the axial direction of the heat transfer tube so that each fin comes close to the adjacent fin, and the bent tips provide gaps between the fins and the adjacent fins, thus forming the cavities.

Description

  The present invention is incorporated in a falling liquid film evaporator, and is suitable for causing heat exchange with a heat source medium while allowing unvaporized liquid refrigerant to flow down on the heat transfer pipe. And a turbo refrigerator using the same.

  In general, a full liquid evaporator and a falling liquid film evaporator are known as evaporators used in a relatively large capacity refrigeration cycle.

  In a full liquid evaporator, it is necessary to enclose a lot of liquid refrigerant so that the heat transfer tube is immersed in the liquid refrigerant. In addition, since the heat transfer performance is significantly changed by the heat load, the performance at the time of low heat load is remarkably deteriorated. In addition, since a load corresponding to the head pressure is applied, a loss corresponding to this occurs in the low-pressure refrigerant. On the other hand, the falling liquid film evaporator requires a pump for spraying the refrigerant, and it is extremely important to increase the pump power and to ensure the wetting of the refrigerant on the heat transfer tube. It has become.

  In order to solve this problem, various heat transfer tubes for falling liquid film evaporators have been studied. For example, there are proposed ones in which a large number of protrusions and fins are formed on the outer surface of the heat transfer tube (see Patent Document 1), and one step further in which a hollow portion is formed on the outer surface of the heat transfer tube (see Patent Document 2). . In particular, in Patent Document 2, the first fins having short heights and the second fins having high heights are alternately formed on the outer surface of the heat transfer tube, and the tip of the second fin having the taller height is formed. A hollow portion is formed in which an inflow port (gap) is provided between the first fin and the second fin by being bent and brought close to the tip of the first fin.

Japanese Patent Laid-Open No. 9-61080 (FIGS. 2, 5, and 6) Japanese Patent Laying-Open No. 2005-121238 (FIGS. 1 to 3)

  In the falling liquid film evaporator, the pump, the spreader, and the power for operating the pump are required to spray the refrigerant, leading to a decrease in COP (coefficient of performance) and increasing the cost of the equipment. If the performance of the heat exchanger can be improved more than the power of the pump, the same COP as in the case of the full liquid type can be obtained. Furthermore, the reduction of the refrigerant filling amount is significant when considering future environmental problems, and brings about an effect more than the cost increase of equipment.

  However, the thing of patent document 1 which formed the protrusion and the fin in the outer surface of the heat exchanger tube has not enough heat exchange performance. Further, in Patent Document 2 in which a hollow portion is formed on the outer surface of the heat transfer tube, a pair of fins having different heights are formed, and the hollow portion is formed by bending only the taller fin. However, the formation method is not easy. Therefore, there is still room for improvement in order to apply these to the heat transfer tube for a falling liquid film evaporator or to employ it in a turbo refrigerator.

  An object of the present invention is to provide a heat transfer tube for a falling film evaporator that has a simple structure and is easy to form, and a high-performance turbo refrigerator using the heat transfer tube.

According to one embodiment of the present invention, in the heat transfer tube for the falling liquid film evaporator, which is formed in a tubular shape and configured to evaporate the falling liquid film on the outer surface of the tube,
A plurality of fins continuously formed annularly or spirally in the circumferential direction of the outer surface of the heat transfer tube;
Each fin is bent so that the tip of each fin is close to the adjacent fin, and is formed substantially parallel to the tube axis direction of the heat transfer tube, and a gap is formed between the bent fin and the adjacent fin. A plurality of cavities,
A heat transfer tube for a falling film evaporator is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the heat transfer tube for falling liquid film type evaporators with a simple structure and easy formation, and a high performance turbo refrigerator using the same can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a partial explanatory view which shows the pipe | tube outer surface shape of the heat exchanger tube for liquid film type evaporators concerning one embodiment of this invention, (a) is a perspective sectional view, (b) is a top view, (c) is a front section. FIG. It is explanatory drawing which shows the manufacturing process of the heat exchanger tube for falling liquid film type evaporators concerning one embodiment of this invention, (a) is a fin formation process figure, (b) is a notch part formation process figure, (c) ) Is a process for forming a cavity. It is a schematic block diagram of the evaporation performance evaluation apparatus which implements the evaporation performance evaluation method for evaluating the heat exchanger tube for falling film type evaporators concerning one embodiment of the present invention. It is explanatory drawing which shows one specific example of the evaluation result obtained by the evaporation performance evaluation method, and the heat flux and the evaporation heat when the heat transfer tube for the falling film type evaporator of the embodiment is commonly used for the flowing type and the full type It is a figure which shows the relationship with a transmission rate. It is explanatory drawing which shows a specific example of the evaluation result obtained by the evaporation performance evaluation method, and is a figure which shows the relationship between the heat flux and evaporation heat transfer coefficient in an Example and a comparative example. It is explanatory drawing which shows the pipe | tube outer surface shape of the heat exchanger tube for falling liquid film type evaporators of a comparative example, (a) is the comparative example 1 which has a projecting fin, (b) is the comparative example 2 which has a linear fin, ( c) is a perspective view of a comparative example 3 having spiral fins. It is a mimetic diagram showing an example of the turbo refrigerator provided with the falling liquid film type evaporator concerning one embodiment of the present invention. It is a schematic diagram which shows the structure of the refrigerator provided with the general full liquid evaporator.

  An embodiment of the present invention will be described with reference to the accompanying drawings.

<First embodiment>
[Heat transfer tube for falling film evaporator]
FIG. 1 is a partial explanatory view showing a tube outer surface shape of a heat transfer tube for a falling liquid film evaporator according to an embodiment of the present invention.

  The heat transfer tube for the falling liquid film type evaporator is formed in a tubular shape, forms a liquid film on the heat transfer tube while the non-evaporated liquid refrigerant flows around the heat transfer tube, performs boiling evaporation on the heat transfer tube, and transfers the heat transfer tube. It has a function of exchanging heat with a heat source medium flowing inside the heat pipe.

The falling liquid film evaporator heat transfer tube having such a function includes a cavity portion formed of fins on the surface. A plurality of fins are continuously formed in a ring shape or a spiral shape in the tube circumferential direction on the outer surface of the heat transfer tube. The hollow portion is bent substantially parallel to the tube axis direction of the heat transfer tube so that the tip portion of each fin is close to the adjacent fin, and a gap is provided between the bent tip portion and the adjacent fin. A plurality are formed. A notch is formed at a predetermined interval along the continuous direction of the fin at the tip of the fin, and the cavity is formed between the notch formed at the tip and the tip and the adjacent fin. The gap is formed so as to communicate with the outside.

In some embodiments, the fins and cavities are formed by processing a heat transfer tube.
In the heat transfer tube for a falling liquid film evaporator according to the embodiment shown in FIG. 1, for example, the heat transfer tube described below is processed by processing the heat transfer element surface of the copper heat transfer tube main body 30 (a smooth surface before processing). It has an outer shape.

  The plurality of fins 31 are formed by cutting the outer surface of the heat transfer tube main body 30 by cutting. As a result of being formed by shaving, fins 31 that are annularly or spirally continuous in the circumferential direction of the outer surface of the tube (see the arrow in the figure) are raised on the outer surface of the tube corresponding to the outer surface of the heat transfer tube body 30. It is formed in the state. Further, since the fin 31 is formed by shaving, the tip 31a is sharp and formed in a tapered shape. The fin 31 to be bent later is provided with valley-shaped notches 36 formed from the tip end portion 31 a to the base end portion 31 b at predetermined intervals along the continuous direction of the fin 31. Yes. The arrangement of the notches 36 between the fins 31 may be parallel to the tube axis direction, but may be shifted with respect to the tube axis direction as shown.

  The plurality of hollow portions 38 are formed in a plurality of annular shapes continuously in the pipe circumferential direction by bending each fin 31. Each cavity 38 is formed by the inner peripheral surface 38a of the bent fin 31, the rear surface 38b of the adjacent fin 31 bent, and the heat transfer tube outer surface 38c newly exposed by shaving. The bent tip 31a of the fin 31 becomes a new heat transfer surface, and the unfolded base end 31b of the fin 31 forms a heat transfer wall. The bending of the fins 31 is performed so that the tip portions 31 a of the fins 31 are parallel to the tube axis direction of the heat transfer tube body 30. The front end portion 31 a of each fin 31 is bent so as to be close to the adjacent fin 31, and a gap 37 is formed between the bent front end portion 31 a and the adjacent fin 31. The cavity 38 is configured to communicate with the outside through the gap 37 and the notch 36 described above. When the cavity 38 is configured to communicate with the outside by the notch 36 and the gap 37 formed between the tip 31a and the adjacent fin 31, the liquid refrigerant enters the cavity 38. And the discharge of vapor bubbles out of the cavity 38 is facilitated.

  By having such a heat transfer tube outer surface shape, a plurality of hollow portions 38 continuously formed in the tube circumferential direction are formed on the tube outer surface of the falling liquid film evaporator heat transfer tube in the tube axis direction. Line up on the pitch. A gap 37 is arranged in the pipe circumferential direction at the upper end of the cavity 38. Further, a plurality of notches 36 are arranged at a predetermined interval along the continuous direction of each cavity 38, and these notches 36 are arranged so as to be shifted between each cavity 38. In this case, the new heat transfer surface of the cavity portion 38 constituted by the tip portion 31a has a tapered surface, does not have an uneven portion or a groove, and is a smooth surface. Therefore, the heat transfer tube for the falling liquid film evaporator according to the present embodiment, in which the cavity is formed from one fin, has a simpler structure and can be formed as compared with the case where the cavity is formed from a pair of fins having different heights. It becomes easy.

In addition to the above-described structure, the flowing-down liquid film evaporator heat transfer tube described in the present embodiment is provided with a spiral rib 45 on the inner surface of the heat transfer tube main body 30. The formation method of the rib 45 is not particularly limited, and may be performed using a known method. Therefore, the detailed description regarding the formation method of the rib 45 is abbreviate | omitted here. In the falling liquid film evaporator heat transfer tube having such a rib 45 on the inner surface of the tube, compared to the case where the rib 45 is not provided, the falling liquid film evaporator heat transfer tube and the heat source medium flowing in the heat transfer tube are provided. Heat transfer efficiency is improved. Therefore, it contributes to the improvement of the evaporation performance (heat transfer performance) in the heat transfer tube for the falling liquid film evaporator through the improvement of the heat transfer efficiency with the heat source medium.

  In the flowing-down liquid film evaporator heat transfer tube configured as described above, the liquid refrigerant flowing down around the heat transfer tube body 30 is heated on the heat transfer tube body 30. The heated liquid refrigerant is guided into the cavity 38 through the notch 36 and the gap 37 and causes nucleate boiling in the cavity 38. Therefore, the generated boiling nuclei stagnate in the cavity 38, vapor bubbles develop and become large, and are discharged from the notch 36 and the gap 37 to the outside of the cavity 38. Since the liquid refrigerant flowing down is guided into the cavity 38 instead of the vapor bubbles discharged outside the cavity 38, the liquid refrigerant can be prevented from drying out on the heat transfer tube body 30. Therefore, wetting of the refrigerant on the heat transfer tube main body 30 is ensured, and the heat exchange performance of the heat transfer tube main body 30 can be further improved.

  Similarly, in the case of a heat transfer tube for a full liquid evaporator, the heat source medium flowing inside the heat transfer tube is heated, but the heat transfer tube for a full liquid evaporator has a large filling amount of liquid refrigerant. As described above, the necessary energy is more than double that of the flow-down type, which is not preferable.

  In the embodiment shown in FIG. 1, as a specific example, the arrangement pitch P between the cavity portions 38 adjacent in the tube axis direction of the heat transfer tube is 0.4 mm or more and 0.8 mm or less, and the cavity portion 38. The depth D is 0.2 mm or more and 0.8 mm or less. When the arrangement pitch P between the hollow portions 38 in the tube axis direction is too narrow than 0.4 mm, the boiling region decreases, and conversely, when the pitch P is too wide than 0.8 mm, the base end portion 31b serving as a heat transfer wall is formed. Therefore, the arrangement pitch P between the hollow portions 38 is preferably 0.4 mm or more and 0.8 mm or less. On the other hand, if the depth D of the cavity 38 is too shallow than 0.2 mm, it becomes difficult to keep the boiling nuclei stagnant. Conversely, if the depth D is too deep than 0.8 mm, the heat transfer wall (base end portion 31 b). Therefore, the heat transfer from the bottom is preferably 0.2 mm or more and 0.8 mm or less.

  Moreover, it is preferable that the width G of the gap 37 formed between the tip portion 31a where the notch portion 36 is not formed and the adjacent fin 31 is 0.05 mm or more and 0.5 mm or less. If the width G of the gap 37 is too narrow than 0.05 mm, it becomes a resistance to inflow of liquid refrigerant, and if it is too wide than 0.5 mm, the liquid refrigerant cannot remain in the cavity 38, so that it is 0.05 mm or more. 0.5 mm or less is preferable.

[Method for manufacturing heat transfer tube for falling film evaporator]
The falling-film-film evaporator heat transfer tube of the above-described embodiment can be manufactured by the method shown in FIG.

  First, as shown in FIG. 2 (a), a heat transfer tube main body 30 having a smooth outer surface and a grooved inner surface is prepared, a cutting tool 32 having a cutting edge angle of 60 ° is used, and a predetermined cutting angle is obtained. The cutting tool 32 is rotated in the circumferential direction and the heat transfer tube body 30 is moved in the tube axis direction so that the fins 31 are shaved up so that the cut amount and the interval between the formed fins 31 have predetermined dimensions. . Here, the cutting angle of the cutting tool 32 was 24 °, and the cutting amount of the cutting tool 32 was 0.20 mm. Further, the rotational speed of the cutting tool 32 and the feed speed of the heat transfer tube main body 30 were adjusted so that the arrangement pitch P of the hollow portions 38 in the tube axis direction was 0.5 mm.

  Next, as shown in FIG. 2 (b), the grooved roll 34 is rotated in the circumferential direction, the heat transfer tube is moved in the tube axis direction, and the fin 31 is pressed by the grooved roll 34 to move the tip 31a. A notch 36 having a depth of 0.2 mm was formed at 45 ° with respect to the tube axis direction.

Further, as shown in FIG. 2C, the flat roll 35 is rotated in the circumferential direction, the heat transfer tube is moved in the tube axis direction, and the fins 31 are pressed by the flat roll 35 to have a cavity portion 38 having a gap 37. Formed. Here, the depth D of the cavity 38 is 0.5 mm, and the width G of the gap 37 is 0.
. The amount by which the flat roll 35 was pushed in was adjusted to 1 mm.

    As described above, according to the method of manufacturing a heat transfer tube for a falling liquid film evaporator according to the present embodiment, fins are formed by shaving with a cutting tool, cutout portions are formed with grooved rolls, and hollow portions are formed with flat rolls. By simply executing the three steps of forming, it is possible to easily create a falling liquid film evaporator heat transfer tube having the shape of the outer surface of the heat transfer tube of the present embodiment.

[Evaporation performance evaluation equipment]
The heat transfer performance of the heat transfer tube (test tube 8) thus obtained was evaluated using the evaporation performance evaluation apparatus shown in FIG. This evaluation apparatus has a structure in which an evaporator 6 and a condenser 5 made of a SUS shell having a length of 300 (mm) are connected by a pipe 7.

  In the evaporator 6, five test tubes 8 are installed in the vertical direction, and a spray tube 9 is installed on the top. The lower part of the evaporator 6 was filled with the liquid refrigerant 11 so as not to touch the test tube 8 arranged in the lower stage. A conduit 12 is connected to the lower part of the evaporator 6, and the liquid refrigerant 11 filled in the evaporator 6 passes through the conduit 12 and is supplied by a pump 13 to a spray pipe 9 disposed in the evaporator 6. The liquid refrigerant is sprayed on the test tube 8. The pump 13 is driven via an inverter, and the pump discharge amount is adjusted by the inverter, and the spray amount is monitored by the flow meter 14 arranged between the pump 13 and the spray pipe 9. .

  The evaporation performance of the test tube 8 is evaluated by passing hot water as a heat source medium from the inlet to the outlet in the test tube 8, and the temperature of the hot water at the inlet and outlet is a platinum resistance thermometer 15a, which is an example of a thermometer. 15b. The flow rate of the hot water is measured by the electromagnetic flow meter 16.

  The spray tube 9 is provided with holes of φ1.5 (mm) at intervals of 15 (mm) in the tube axis direction, from which liquid refrigerant is sprayed onto the test tube 8, and further outside the test tube 8. On the surface, the liquid refrigerant is heated by the hot water passed through the pipe, and the liquid refrigerant starts to evaporate and becomes a gas refrigerant.

  The condenser 5 is provided with five condensation promoting heat transfer tubes 10 in the horizontal direction. In these condensation promotion heat transfer tubes 10, the brine is configured to flow from the inlet side toward the outlet side. By this brine, the outer surface of the condensation-accelerating heat transfer tube 10 is cooled below the saturation temperature of the refrigerant vapor. The inlet / outlet temperature of the brine is measured by platinum resistance thermometers 15c and 15d which are an example of a thermometer. The condenser 5 is connected to a pressure gauge 17 for measuring the pressure within the diameter.

  The gas refrigerant that has risen from the evaporator 6 through the pipe 7 to the condenser 5 is condensed and liquefied by the condenser 5, and descends the pipe 7 to be collected by the evaporator 6.

[Evaporation performance evaluation of test tubes]
Specifically, the evaporation performance of the test tube 8 was evaluated under the following conditions.

  First, the test tube 8 was set in the evaporator 6 and the system was evacuated, and then R134a serving as a liquid refrigerant was sealed.

  Next, hot water as a heat source medium adjusted so that the inlet temperature becomes a predetermined temperature is passed through the test tube 8 at a flow rate adjusted to 1.5 (m / s). Thereafter, the pump 13 is rotated, and the liquid refrigerant 11 is sprayed on the test tube 8 from the spray pipe 9 constituting the liquid refrigerant spray device.

  Thereafter, the temperature and flow rate of the brine flowing into the condensation promotion heat transfer tube 10 in the condenser 5 were controlled so that the indicated value of the pressure gauge 17 was, for example, a refrigerant saturation temperature of 5 ° C.

  When the liquid refrigerant is sprayed from the spray tube 9 in the evaporator 6, the outer surface of the test tube 8 is heated above the vaporization temperature of the liquid refrigerant by the hot water flowing in the test tube 8. The liquid refrigerant in contact with the outer surface of the tube evaporates and becomes gaseous.

  In the evaluation step, the heat transfer coefficient on the outer surface of the test tube 8 is measured when the test tube 8 evaporates the liquid refrigerant in the evaporation step. The method for measuring the heat transfer coefficient is not particularly limited, and may be performed using a known method. Therefore, the detailed description regarding the measurement method is omitted here.

  FIG. 4 is a view showing the relationship of heat transfer performance when the heat transfer tube for the falling liquid film evaporator according to this embodiment is commonly used for the falling liquid film evaporator and the full liquid evaporator. FIG. 5 is a graph comparing the relationship between the amount of refrigerant sprayed and the evaporation heat transfer coefficient for the falling liquid film evaporator heat transfer tube of this example and the full liquid evaporator heat transfer tube of the comparative example. Note that. The full liquid evaporator and the falling liquid film evaporator will be described later (see FIGS. 7 and 8).

  As is clear from FIG. 4, the heat transfer tube for the falling liquid film evaporator according to the example shows higher heat transfer performance than the boiling promotion tube used in the full liquid evaporator, and has a low heat load (at a low heat flow rate). ), High heat transfer performance can be obtained. In addition, heat transfer performance similar to the full liquid type can be ensured even at high heat load (at high heat flow rate).

  Moreover, from FIG. 5, the heat-transfer pipe | tube for falling liquid film type evaporators by an Example shows high heat-transfer performance compared with the case of each heat-transfer pipe | tube of the comparative examples 1, 2, and 3. FIG. Here, Comparative Examples 1, 2, and 3 are a heat transfer tube (FIG. 6 (a)) having a large number of protrusions on the surface, a heat transfer tube having fins in the longitudinal direction of the heat transfer tube (FIG. 6 (b)), and a spiral. It means a heat transfer tube having fins in a shape (FIG. 6C). The heat transfer pipe for a falling liquid film evaporator according to the embodiment can also control the heat transfer performance, which is difficult with a full liquid evaporator, by changing the refrigerant spray amount. Therefore, if it is configured so that the amount of liquid refrigerant sprayed from the liquid refrigerant spraying device can be adjusted, heat exchange suitable for the falling liquid film evaporator heat transfer tube can be performed. It is possible to ensure sufficient.

[Effect of the first embodiment]
The embodiments of the present invention have one or more of the following effects.
(1) According to one embodiment of the present invention, in the heat transfer tube for a falling liquid film evaporator, a plurality of fins continuously formed in an annular shape or a spiral shape in the circumferential direction of the outer surface of the heat transfer tube; A plurality of fins formed by bending the tip of each fin in parallel with the tube axis direction of the heat transfer tube so as to be close to the adjacent fin, and providing a gap between the bent fin and the adjacent fin. And a heat transfer tube for a falling liquid film evaporator provided with a hollow portion. With this configuration, the liquid refrigerant flowing around the heat transfer tube is heated on the heat transfer tube, and the heated liquid refrigerant is guided into the cavity from the gap, causing nucleate boiling in the cavity. . Therefore, the generated boiling nuclei are stagnated in the cavity, and vapor bubbles develop and become larger, and are released from the gap to the outside of the cavity. Since the flowing liquid refrigerant is guided into the cavity instead of the vapor bubbles released outside the cavity, it is possible to prevent the liquid refrigerant from drying out on the heat transfer tube. Therefore, wetting of the refrigerant on the heat transfer tube is ensured, and the heat exchange performance of the heat transfer tube can be further improved. In addition, the falling liquid film evaporator heat transfer tube of the present embodiment, in which each fin is bent to form a cavity, has a simpler structure than that in which every other fin is bent to form a cavity. Will also be easier.

(2) In this case, it is preferable that the fin is formed by shaving the outer surface of the heat transfer tube with a cutting tool such as a cutting tool. Fins can also be formed by rolling, but if the fins are formed by cutting with a cutting tool, a heat transfer surface can be easily formed on the outer surface of the heat transfer tube.

(3) Moreover, it is preferable that the said cavity part is formed by pressing a flat roll against the said fin and bending the front-end | tip part of the said fin. By bending the tip of the fin using a flat roll, a cavity can be easily formed on the outer surface of the heat transfer tube.

(4) Moreover, the notch part is formed in the front-end | tip part of the said fin at predetermined intervals along the continuous direction of the said fin, The said cavity part has the notch part formed in the said front-end | tip part, and the said notch part Is configured to communicate with the outside by a gap formed between the tip portion where the heat sink tube is not formed and the adjacent fin, and the arrangement pitch between the cavity portions adjacent in the tube axis direction of the heat transfer tube is It is preferably 0.4 mm or more and 0.8 mm or less, and the depth of the cavity is preferably 0.2 mm or more and 0.8 mm or less. Thus, when the cavity is configured to communicate with the outside by the notch and the gap formed between the tip and the adjacent fin, the liquid refrigerant is guided into the cavity, and Emission of vapor bubbles out of the cavity is facilitated. In this case, if the arrangement pitch between the cavities in the tube axis direction is too narrow than 0.4 mm, the boiling region decreases, and conversely, if it is too wide than 0.8 mm, it is from the fin that becomes the heat transfer wall. Since heat transfer worsens, 0.4 mm or more and 0.8 mm or less are preferable. Moreover, if the depth of the cavity is too shallow than 0.2 mm, it is difficult to keep the boiling nuclei stagnant. Conversely, if the depth of the cavity is too deep than 0.8 mm, heat transfer from the heat transfer wall becomes worse. 0.2 mm or more and 0.8 mm or less is preferable.

(5) Moreover, it is preferable that the said notch part is formed by pressing a grooved roll to the front-end | tip part of the said fin. By thus pressing the tip of the fin using the grooved roll, a notch communicating with the outside can be easily formed in the cavity.

(6) Moreover, it is preferable that the said clearance gap formed between the front-end | tip part in which the said notch part is not formed, and the said adjacent fin is 0.05 mm or more and 0.5 mm or less. If the gap is too narrow than 0.05 mm, it becomes a resistance to inflow of the refrigerant liquid, and if it is too wide than 0.5 mm, the refrigerant liquid cannot remain in the cavity, so 0.05 mm or more and 0.5 mm or less is preferable. .

(7) Moreover, it is preferable that the spiral rib is provided in the inner surface of the said heat exchanger tube. When the spiral rib is provided on the inner surface of the heat transfer tube, the heat transfer of the heat source medium flowing inside the heat transfer tube is promoted.

(8) According to the falling-film-film heat exchanger tube having part or all of the above-described configuration, extremely good heat transfer performance can be obtained even at low heat loads. Moreover, since the heat transfer performance similar to the full liquid type can be ensured even under a high heat load, the turbo refrigerator can be improved in performance. At the same time, since it is a falling film type heat exchanger, the amount of refrigerant enclosed can be reduced.

  In addition to the above, it is needless to say that the heat transfer tube for the falling liquid film evaporator according to the present embodiment can be variously modified without departing from the gist thereof. For example, in the embodiment, the heat transfer surface is formed by shaving the fin with a cutting tool, but the heat transfer surface can also be formed by a method by rolling.

<Second Embodiment>
[Refrigerator using falling liquid film evaporator]
FIG. 7 shows a refrigerator equipped with the heat transfer tube for a falling liquid film evaporator according to the above-described embodiment. The gas refrigerant discharged from the compressor 18 is condensed and liquefied by the condenser 19, then becomes a gas-liquid two-phase state by the expansion valve or the throttle valve 24, and is evaporated through the distribution plate 23 provided at the lower part of the evaporator 20. The structure is supplied to the container 20. Inside the evaporator 20, a large number of falling liquid film evaporator heat transfer tubes 21 through which the heat source medium flows are installed, and the upper part thereof prevents the inflow of droplets accompanying the rising gas refrigerant 26 into the compressor. In order to do so, an eliminator 22 is provided.

  A spray pipe 29 is installed on the upper part of the many falling liquid film evaporator heat transfer pipes 21 installed in the evaporator 20, and the spray pipe 29 and the liquid refrigerant 25 accumulated in the lower part of the evaporator 20 are connected by a conduit 28. R134a is supplied as a liquid refrigerant by a circulation pump 27 provided in the conduit 28. The circulation pump 27 is driven through an inverter (not shown), and the pump discharge amount is adjusted by the inverter. Further, a flow meter (not shown) for monitoring the flow rate of the liquid refrigerant 25 is disposed in the path of the conduit 28 between the circulation pump 27 and the spray pipe 29, and the pump discharge amount is based on the monitoring result. Is configured so that the supply amount of the liquid refrigerant 25 to the spray tube 29 can be adjusted. The above-described spray pipe 29, conduit 28, circulation pump 27, and flow meter constitute a liquid refrigerant spray device.

  Further, the gas / liquid two-phase liquid refrigerant 25 that has flowed out of the expansion valve or the throttle valve 24 from the condenser 19 is supplied to the lower part of the evaporator 20, and together with the liquid refrigerant circulated from the lower part of the evaporator 20. It is sprayed on the heat transfer tube 21.

  When spraying R134a from the spray tube 29, the supply amount of R134a to the spray tube 29 is adjusted through control of the pump discharge amount so that the spray amount becomes a desired amount. By controlling the amount of R134a sprayed from the spray tube 29 in this way, the amount of R134a covering the outer surface of the falling liquid film evaporator heat transfer tube 21 is adjusted.

  The liquid refrigerant sprayed and flowed down from the spray tube 29 evaporates by exchanging heat with the heat source medium flowing inside the test tube 8 while forming a thin liquid film on the outer surface of each heat transfer tube 21. In such a falling liquid film type evaporator, the amount of refrigerant in the evaporator may be several times the amount of evaporation according to the heat load, so the amount of refrigerant is very small compared to a full liquid type evaporator. I'm sorry. Therefore, it is possible to reduce the amount of refrigerant enclosed in the turbo refrigerator. In addition, it is possible to realize a turbo chiller that uses a falling liquid film evaporator heat transfer tube suitable for heat exchange with a heat source medium while causing unvaporized liquid refrigerant to flow down on the heat transfer tube. This makes it possible to provide a turbo chiller with higher performance than the heat transfer tubes for full liquid evaporators.

[Full liquid evaporator as a comparative example]
A refrigerator equipped with a full liquid evaporator is shown in FIG. The configuration of the refrigeration cycle is the same as that of the flow-down type, but a large number of heat transfer tubes 21 through which the heat source medium flows are installed in the evaporator 20 so as to be immersed in the liquid refrigerant 25. The full-liquid evaporator having such a structure has excellent heat transfer characteristics because heat exchange with the heat source medium flowing inside the heat transfer tube is performed by boiling heat transfer actively generated on the outer surface of the heat transfer tube. On the other hand, it is necessary to enclose a large amount of liquid refrigerant in the evaporator so that the heat transfer tube is immersed in the liquid refrigerant.

[Effect of the second embodiment]
According to the present embodiment, the heat transfer tubes for the falling liquid film evaporator described above are arranged as a multi-row heat transfer tube group, and the liquid refrigerant sprayed from the liquid refrigerant spraying device installed at the top of the heat transfer tube group is A falling liquid film evaporator configured to form a liquid film on the outer surface of the heat transfer tube group while flowing down, perform boiling evaporation on each heat transfer tube, and exchange heat with a heat source medium flowing inside each heat transfer tube A turbo chiller is provided. When the falling liquid film evaporator to which the heat transfer pipe for the falling liquid film evaporator is applied as described above is adopted in the turbo chiller, the performance of the heat exchanger exceeds the power of the pump necessary for spraying the liquid refrigerant. Since it is possible to improve, it is possible to achieve high performance at low cost compared to a turbo chiller employing a full liquid evaporator. In addition, good heat transfer performance can be obtained even at low heat loads, and heat transfer performance similar to the full liquid type can be secured even at high heat loads, so that the performance of the turbo refrigerator can be improved.

30 Heat Transfer Tube Body 31 Fin 31a Tip 31b Base End 32 Bite 34 Grooved Roll 35 Flat Roll 36 Notch 37 Gap 38 Cavity 45 Rib

Claims (9)

In the heat transfer tube for the falling liquid film evaporator, which is formed in a tubular shape and configured to boil and evaporate the falling liquid film on the outer surface of the pipe
A plurality of fins continuously formed annularly or spirally in the circumferential direction of the outer surface of the heat transfer tube;
Each fin is bent so that the tip of each fin is close to the adjacent fin, and is formed substantially parallel to the tube axis direction of the heat transfer tube, and a gap is formed between the bent fin and the adjacent fin. A plurality of cavities,
A heat transfer tube for a falling liquid film evaporator. Notch portions are formed at predetermined intervals along the continuous direction of the fins at the tip portions of the fins,
The cavity is communicated to the outside by a notch formed in the tip and a gap formed between the tip not formed with the notch and the adjacent fin. Configured,
The arrangement pitch between the hollow portions adjacent in the tube axis direction of the heat transfer tube is 0.4 mm or more and 0.8 mm or less, and the depth of the hollow portion is 0.2 mm or more and 0.8 mm or less. A heat transfer tube for a falling liquid film evaporator as described in 1.   The downflow liquid film evaporator heat transfer tube according to claim 2, wherein the notch is formed by pressing a grooved roll against the tip of the fin.   The heat transfer tube for a falling liquid film evaporator according to any one of claims 1 to 3, wherein the gap formed between the tip portion and the adjacent fin is 0.05 mm or more and 0.5 mm or less.   The heat transfer tube for a falling film evaporator according to any one of claims 1 to 4, wherein the fin is formed by scraping and raising the outer surface of the heat transfer tube with a cutting tool.   The heat transfer tube for a falling liquid film evaporator according to any one of claims 1 to 5, wherein the hollow portion is formed by pressing a flat roll against the fin and bending a tip portion of the fin.   The heat transfer tube for a falling liquid film evaporator according to any one of claims 1 to 6, wherein a spiral rib is provided on an inner surface of the heat transfer tube. In a turbo refrigerator equipped with a falling liquid film evaporator,
The falling liquid film evaporator is installed on a heat transfer tube group in which a plurality of heat transfer tubes for the falling liquid film evaporator according to any one of claims 1 to 7 are arranged, and an upper portion of the heat transfer tube group. A liquid refrigerant spraying device, forming a liquid film on the outer surface of the heat transfer tube group while the liquid refrigerant sprayed from the liquid cooling spraying device flows down, and performing boiling evaporation on each heat transfer tube to each heat transfer tube A turbo refrigerator configured to exchange heat with a heat source medium flowing inside.   The turbo chiller according to claim 8, wherein the liquid refrigerant spraying device is configured so that a spraying amount of the liquid refrigerant sprayed from now on can be adjusted.

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